Add krel release notes validation workflow

[npolshakova]

What type of PR is this:

/kind feature

What this PR does / why we need it:

Adds a GitHub Action to setup krel.

This is required to setup a presubmit job for PRs like: #2659. The current requirement is to add validation using:

$ krel release-notes validate --help
krel release-notes validate

The 'validate' subcommand of krel has been developed to:

1. Check release notes maps for valid yaml.

2. Check release notes maps for valid punctuation.

Usage:
  krel release-notes validate [flags]

Flags:
  -h, --help                           help for validate
      --path-to-release-notes string   The path to the release notes to validate. Can be a top level directory or a specific file.

The release notes team is blocked whenever invalid yaml is merged into sig-release:

#2589
#2541

Invalid yaml can be introduced during the review process when people apply changes or manually edit the maps (not through krel, but in an editor). This workflow automates preventing invalid yaml from merging into sig-release.

Which issue(s) this PR fixes:

Fixes kubernetes/release#2753

Special notes for your reviewer:

Based on @Vyom-Yadav's GitHub workflow: kubernetes-sigs/release-actions#101

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: npolshakova
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[Vyom-Yadav]

/assign